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Aim Schizophrenia is a severe psychiatric disorder with heterogeneous outcomes; factors such as anxiety, childhood trauma, and duration of untreated psychosis (DUP) may influence symptom severity and disease progression. Growing evidence highlights immune dysregulation—particularly alterations in complement components C3 and C4—in the pathophysiology of schizophrenia; however, findings regarding peripheral complement levels and their clinical associations remain inconsistent. Method Thirty-nine patients with schizophrenia underwent clinical assessment using the Childhood Trauma Questionnaire (CTQ), the Positive and Negative Syndrome Scale (PANSS), the State–Trait Anxiety Inventory (STAI), and the Montreal Cognitive Assessment (MoCA). Serum concentrations of C3 and C4 were measured at admission. Results In exploratory analyses (nominal p-values), baseline C3 correlated with DUP (r=0.407, p=0.010) and length of hospitalization (r=0.353, p=0.028). Higher C3 was associated with greater symptom severity on PANSS-P 1 (r=0.325, p=0.043) and PANSS-G 1 (r=0.330, p=0.040), while C4 correlated with PANSS-G 1 (r=0.322, p=0.045) and multiple PANSS domains after 12 weeks. C3 was associated with anxiety at baseline and after 3 months (STAI-T 1 : r=0.376, p=0.018; STAI-S 1 : r=0.372, p=0.020; STAI-T 2 : r=0.376, p=0.018; STAI-S 2 : r=0.419, p=0.009), whereas C4 correlated with STAI-T 1 (r=0.361, p=0.024), STAI-S 1 (r=0.342, p=0.033), and STAI-S 2 (r=0.338, p=0.038). Higher C3 and C4 levels were associated with CTQ subscales. C3 correlated negatively with cognitive performance (MoCA 1 : r=–0.339, p=0.034). However, none of the associations survived Benjamini–Hochberg false discovery rate (BH-FDR) correction (all q>0.05). Conclusion These exploratory, within-cohort findings suggest that peripheral complement markers relate to variation in clinical severity and illness-course indicators in schizophrenia. Replication in larger, controlled longitudinal studies is warranted.